AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020
Commonly Used Symbols
Mathematical Composition
Use mathematical symbols in running text only if they are presented with a numerical value within parentheses. These symbols can be used in figures, tables, and boxes with no explanatory footnotes. Some commonly used symbols are as follows:
Symbol |
Description |
> |
greater than |
≥ |
greater than or equal to |
< |
less than |
≤ |
less than or equal to |
± |
plus or minus (This symbol should not be used to indicate variability around a central tendency, eg, “The control group had a mean [SD] value of 12 [7],” not “The control group had a mean of 12 ± 7.”) |
integral from value of a to value of b |
|
summation from a = 1 to a = 30 |
|
product of a = 1 to a = 30 |
|
Δ |
delta (change, difference between values) |
f |
function |
≠ |
not equal to |
≈ |
approximately equal to |
∼ |
similar to (reserve for use in geometry and calculus, when it can be used in equations to mean “is distributed as”; use words in other cases where “approximately” is meant) |
≅ |
congruent to |
≡ |
defined as |
∴ |
therefore |
∞ |
infinity |
! |
factorial, eg, n! = n(n − 1) (n − 2) . . . 1 |
The following symbols are usually reserved for specific values:
π |
pi (approximately 3.1416; do not confuse with uppercase Π) |
e |
base of the system of natural logarithms (approximately 2.7183; see 20.3.3, Logarithmic Expressions; in statistical equations, however, “e” represents the error term in a regression equation) |
i |
the square root of −1 |
For a list of additional symbols that are used in statistics, see 19.6, Statistical Symbols and Abbreviations.
The following are examples of these commonly used mathematical expressions:
>105 CFUs/mL
24.5 ± 0.5
L ≈ 2 × 1010 m
f (x) = x + Δx
y = dx/dt
P < .001
P < 10 × 3—10 (for very small P values, do not use “e” to represent the exponent; see 19.4.2, Rounding)
r ! (n − r)!
(ex + e−x)/2
Y = β1 + β2 + e
kg ⋅ m ⋅ s−2
(in this case the operation sign is indicated on both sides of the ellipses)
Any symbols rendered in HTML should be compatible across most commonly used browser platforms.